A photosensitive resin composition comprising, as a carrier resin component, an elastomer of chlorinated rubber, styrene-butadiene block copolymer, polyurethane or the like, along with an ethylenic unsaturated compound and a photo-polymerization initiator is useful in producing flexographic printing plate materials, as having good elastomeric characteristics. Many proposals for such compositions have been made, for example, in U.S. Pat. Nos. 2,948,611 and 3,024,180 and Japanese Patent Publication No. 51-43374.
Such known, solid, photosensitive resin plate materials must be developed with halogenated hydrocarbons. Therefore, the development of solid, photosensitive resin plate materials for flexography capable of being developed with water is desired, and some have heretofore been proposed.
In Japanese Patent Application Laid-Open Nos. 51-53903 and 53-10648, there has been proposed a photosensitive resin composition comprising a metal or ammonium salt of a carboxyl group-containing polymer. However, the composition is problematic in that it is liquid and that the water-proofness of the printing plate to be formed by the use of the composition is unsatisfactory. In Japanese Patent Application Laid-Open No. 61-22339, there has been proposed a photo-polymerizable composition comprising a salt of a carboxyl group-containing polymer with a vinyl compound having a secondary or tertiary nitrogen atom. However, the composition is also problematic in that the mechanical strength of the printing plate is insufficient and that it is difficult to produce a printing plate material having low hardness when the composition is used. In order to solve these problems, a photosensitive resin composition has been proposed in Japanese Patent Publication No. 5-6178 and U.S. Pat. No. 5,229,434, which comprises micro gel particles that form ammonium salt structures. The composition proposed therein is said to be developable with water and waterproof and that the mechanical strength of a printing plate to be formed by the use of the composition has been improved. However, in containing such micro gel particles, the composition is problematic when used in producing printing plates in that the particles remain as such on the developed plates or drop off from them with the result that the edges of the relieves formed on the plates after aqueous development thereof shall be rough and the image reproducibility of the printing plates for minor relieves is poor.
The subject matter of the present invention is to develop a photosensitive resin composition for printing plates, which has good image reproducibility, which is developable with water and which is resistant to aqueous ink.